Phosphor bronze strip with excellent press formability

ABSTRACT

The present invention relates to a high-strength copper alloy used for electronic parts such as terminals and connectors, and more particularly, to a high-strength phosphor bronze strip. The present invention provides a phosphor bronze strip with excellent punching formability characterized in that a total content of S (20 to 100 ppm), Mn, Ca, Mg and Al is 50 ppm or less, a phosphor bronze strip with excellent punching formability characterized in that the sum total of lengths of etching imprints is 5 mm/mm 2  or more when a cross-section parallel to the rolling direction is etched, a phosphor bronze strip with excellent punching formability characterized in that a copper sulfide phase exists in a range of 1 to 3% of the microstructure whose cross-section is parallel to the rolling direction and a phosphor bronze strip characterized in that the plastic deformation ratio when subjected to a shearing test with clearance of 4 to 10% is 50% or less.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a high-strength copper alloysused for electronic parts such as terminals and connectors, and moreparticularly, to a high-strength phosphor bronze strip.

[0003] 2. Description of the Related Art

[0004] Phosphor bronze such as C5210, C5191 (JIS alloy number) or copperalloy C2600 (JIS alloy number) has excellent formability and mechanicalstrength, and is therefore widely used as materials for electronic partssuch as terminals and connectors. On the other hand, with remarkableprogress in the manufacturing of unprecedentedly slimmer, or smallerparts than ever in recent years, there is an increasing demand forhigh-strength copper alloys such as beryllium copper, titanium copper,Corson-based alloys. However, there are constraints concerning supplyand demand or commercialization in the market for these high-strengthcopper alloys, which are relatively new as copper alloys for electronicparts. For example, there is a problem in a global standard orientedmarket. Furthermore, the fact that these high-strength copper alloys aremore expensive than conventional copper alloys such as phosphor bronzeis not desirable. From these standpoints, further improvements have beensought in the aspects of strength and formability of phosphor bronze,which is said to have high mechanical strength among conventional copperalloys.

[0005] With regard to formability, punching formability and bendingformability are particularly important. When punch forming is repeated,a punch of the press is worn out by fiction with materials and the shearplane of pressform products deteriorates. Therefore, after presswork isconducted a certain number of times, it is necessary to polish dies andreadjust the dies. Since the press speed is also higher from theviewpoint of improving productivity, the importance of a material tomake less wear of the dies during punching process is increasingfurther.

[0006] Furthermore, with miniaturization of contacts, the material isrequired to have higher strength, and at the same time bending isperformed under severe conditions with a small bending radius, which islikely to cause cracking in the bent part. Furthermore, the punchingformability and bending formability are mutually contradictorycharacteristics, and there is a tendency from a sensuous viewpoint thata brittle material is easy to be punched but easy to be cracked, while aductile material is easy to be bent but hard to be punched causing thedies to wear sooner.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide a phosphorbronze strip with improved press formability, especially punchingformability and bending formability required for pressform of electronicparts such as connector terminals. It is another object of the presentinvention to provide a technology to achieve higher strength whilemaintaining the improved press formability.

[0008] The present inventors have improved the above-described pressformability drastically by adjusting components, microstructure andmanufacturing conditions of a phosphor bronze strip.

[0009] That is, the invention comprises the following preferred Aspects:

[0010] (1) A phosphor bronze strip with excellent punching formabilitycharacterized by comprising 20 to 100 mass ppm S, 50 mass ppm or less,in total, of one, two, or more selected from among Mn, Ca, Mg and Al.

[0011] (2) A phosphor bronze strip with excellent punching formability,characterized in that the sum total of lengths of etching imprints whena cross-section parallel to rolling direction is etched is 5 mm/mm² orless.

[0012] (3) A phosphor bronze strip with excellent punching formability,characterized in that a copper sulfide phase exists in a range of 1 to3% of a microstructure of a cross-section parallel to rolling direction.

[0013] (4) The phosphor bronze strip according to any of Aspects (1) to(3), characterized in that a plastic deformation ratio when a shearingtest is conducted with clearance of 4 to 10% is 50% or less.

[0014] (5) A phosphor bronze strip with excellent bending formabilityand punching formability, characterized by comprising 20 to 100 mass ppmS, 50 mass ppm or less, in total, of one, two, or more selected fromamong Mn, Ca, Mg and Al, 100 to 1,000 mass ppm Zn.

[0015] (6) A phosphor bronze strip with excellent bending formabilityand punching formability, characterized in that a mean grain size (mGS)after annealing for 10,000 seconds at 425° C. is 5 μm or less, astandard deviation of the grain size (σGS) is ⅓ mGS or less and adifference between tensile strength and 0.2% yield strength of thecold-rolled phosphor bronze strip is within 80 MPa.

[0016] (7) The phosphor bronze strip with excellent bending formabilityand punching formability according to any of Aspects (1) to (5),characterized in that a mean grain size (mGS) after annealing for 10,000seconds at 425° C. is 5 μm or less, a standard deviation of the grainsize (σGS) of variations in the grain size is ⅓ mGS or less and adifference between tensile strength and 0.2% yield strength of thecold-rolled phosphor bronze strip is within 80 MPa.

[0017] (8) A phosphor bronze strip with excellent bending formabilityand punching formability, characterized in that a cold-rolled strip witha reduction ratio of 45% or more is final recrystallization annealed tothe extent that the mean grain size (mGS) of 3 μm or less and avariation standard deviation (σGS) of 2 μm or less, and then finalcold-rolled with a reduction ratio of 10 to 45%.

[0018] (9) The phosphor bronze strip with excellent bending formabilityand punching formability according to any of Aspects (1) to (5),characterized in that a cold rolled strip with a reduction ratio of 45%or more is final recrystallization annealed to the extent that the meangrain size (mGS) of 3 μm or less and a variation standard deviation(σGS) of 2 μm or less, and then final cold rolled with a reduction ratioof 10 to 45%.

[0019] (10) The phosphor bronze strip with excellent bending formabilityand punching formability according to any of Aspects (1) to (9),characterized in that a cold rolled material with a reduction ratio of X(%) having tensile strength of TS_(o) (MPa) is stress relief annealeduntil tensile strength TS_(a) (MPa) becomes TS_(a)<TS_(o)−X.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] (1) With punching work, a starting point of crack is formed in aportion to be shear deformed in the process of shearing a sheet materialor a strip material using a punch and a die, that is, in a punch strokestep. With this starting point of crack as the starting point, a crackpropagates through the shear deformation part, penetrates the sheet andthereby punching is performed. During this period until a crack starts,the edges of the punch and the die friction strongly with the surface ofthe material. At this time, abrasive wear with the surface of thematerial and scratch wear by foreign particles occur on the edge of thedies and the edge wears out gradually. Therefore, it is desirable thatcracks occur in the shearing process as soon as possible.

[0021] On the other hand, if S exists in phosphor bronze, since thesolubility of S into phosphor bronze is low (see phase diagram of Cu-Ssystem), a Cu₂S phase appears in the matrix. Since Cu₂S phase is morebrittle than, the Cu₂S phase can become a starting point of crack in thematrix during shearing deformation. Adding 20 ppm or more of S canhasten the starting timing of crack. Basically, the greater the contentof S, the better. But if more than 100 ppm of S is added, the bendingformability of a sheet and strip products and the rolling formability inthe process of manufacturing a sheet and strip products worsen, and sothe amount of S to be added is determined to 100 ppm or less.

[0022] By the way, S is not only added as a raw material of coppersulfide, etc., but also included in charcoal carbon that contacts liquidmetal during melting or casting of a phosphor bronze raw material andextreme-pressure agent in press oil in a scrap, etc., and therefore itis effective to intentionally control a mix in of S from thesematerials.

[0023] Mn, Ca, Mg and Al are mixed in as contaminants in theabove-described manufacturing process instead of normal additionalelement of phosphor bronze. However, containing a total of more 50 ppmof these elements prevents the aforementioned Cu₂S phase from scatteringwith functioning as a starting point of crack stably, and therefore itis necessary to control the contents to 50 ppm or less in total.

[0024] (2) On the other hand, when the cross-section of the material isetched using a sulfuric-acid-based etchant reagent, etc., the sulfidephase including copper sulfide is etched preferentially forming finepit-shaped depressed imprints. When this cross-section is observed as adark field image using an optical microscope, etching imprints appearscattered as white dots or lines. When a cross-section parallel to therolling direction is etched with an aqueous solution of sulfuric acid ata normal temperature for a few to 30 seconds and then observed using theabove-described method, if the sum total of lengths of the etchingimprints observed is 5 mm or more per a cross-section of 1 mm², thepunching formability of the phosphor bronze strip is improvedconsiderably for the same reason as that in (1).

[0025] (3) Furthermore, it is possible to calculate the thickness of thecopper sulfide phase from the section parallel to the rolling directionusing the following method and estimate the area ratio of the coppersulfide phase. With an EPMA acceleration voltage set to 15 kV and thediameter of an electron beam on the surface of a sample adjusted to 1μm, a variation of X-ray intensity of sulfur when a beam crosses thecopper sulfide phase is measured. The distance measured after the X-rayintensity rises from the background, reaches a peak and returns to thebackground is defined as the thickness of the copper sulfide phase. Thelength of the copper sulfide phase was measured from a SEM and the areaof the copper sulfide phase was calculated. As a result, it is desirableto determine the total area of the copper sulfide phase to 1 to 3% ofthe whole area. This is because no improvement in the punchingformability would be observed with the area smaller than this, anddetriments such as reduction in the bending formability would bequestioned with the area greater than this.

[0026] (1) to (3) are identical in attempting to take advantage of theeffectiveness of the Cu₂S phase in the phosphor bronze as a startingpoint of crack during shear deformation. However, while they aremutually correlated, they do not always hold a uniquely definedcorrelation. That is, solubility, shape and size of the copper sulfidephase and distribution statue of the copper sulfide phase in phosphorbronze with the same content of S vary depending on a combination ofheat treatment and rolling in the manufacturing process.

[0027] (4) The formability of press punching can also be determined by aplastic deformation rate calculated from the amount of plasticdeformation through a shearing test. The amount of plastic deformationrefers to a distance of a punch movement after a starting point of crackis formed in the shear deformation part, a crack propagates through theshear deformation part with this starting point of crack as the startingpoint until the crack penetrates the sheet. The plastic deformation rateis a value (%) obtained by dividing the amount of plastic deformation bythe thickness of the sheet and is generally applicable. A shearing testis conducted by attaching an upper die (punch) of a shearing tester to across head of a tensile testing machine, letting the upper die down to amaterial on a lower die (die) to punch out a hole of a certain diameter,measuring the punch stroke at this time using a elongation gauge,measuring the punch load using a load cell of the tensile testingmachine and creating a displacement-load curve. The initial linearportion of the displacement-load curve corresponds to an elasticdeformation area and the curve then shows a shear deformation and theload descends linearly when rupture takes place. The amount of plasticdeformation is a distance between a point of deviation from the straightline of the initial elastic deformation area and a point of deviationfrom the load descending straight line at the time of rupture. Sinceclearance has a large influence on the sheet thickness of the materialduring a measurement of the amount of plastic deformation, it isnecessary to select a punch that makes the clearance 4 to 10%. Thephosphor bronze strip having an elastic deformation ratio of 50% or lesscan reduce wear of the dies during high-speed press for manufacturingconnector contacts, etc. ps (5) As described above, the phosphor bronzestrip characterized by comprising 20 to 100 mass ppm S, 50 mass ppm orless, in total, of one, two, or more selected from among Mn, Ca, Mg andAl has favorable punching formability by scattering the copper sulfidephase into the matrix. Part of the copper sulfide in the phosphor bronzewith 100 to 1,000 ppm of Zn changes to zinc sulfide, which promotes asegmentation of the sulfide phase in the reducing thickness process byrepeating rolling and annealing. This segmentation of the sulfide phaseimproves bending formability and provides phosphor bronze, which isexcellent in both punching formability and bending formability. When Znis less than 100 ppm, the copper sulfide changes less to zinc sulfideand bending formability is not improved. When Zn is more than 1,000 ppm,the punching formability deteriorates due to a reduction of the coppersulfide phase, and therefore the amount of Zn added is preferablydetermined to 100 to 1,000 ppm.

[0028] (6) The phosphor bronze in the present invention is defined ashaving a mean grain size (mGS) after annealing for 10,000 seconds at425° C. of 5 μm or less, a standard deviation of the grain size (σGS) of⅓ mGS or less and a difference between tensile strength and 0.2% yieldstrength of the cold rolled copper alloy strip of within 80 MPa.

[0029] By the way, in the present invention the grain size is measuredusing the intercept method based on JTS H 0501. More specifically, thenumber of crystal grains, which are completely crossed by a straightline segment of a predetermined length, is counted and an average valueof the cutting lengths is considered as the grain size. A standarddeviation of the grain size, which is an index of the uniformity, is nota standard deviation of the cutting length but a standard deviation ofthe grain size.

[0030] With a final product subjected to grain boundary strengtheningand dislocation strengthening, that is, strengthened by heat treatmentand rolling, it is not possible to expose the grain boundary. When ametal strip is deformed by cold working, a difference in localtransgranular deformations becomes more remarkable as the deformationprogresses and various deformation bands such as shear band andmicroband appear. These deformation zones make discontinuous therecrystallized gain boundary before cold working and even if itscross-section is etched and observed using an optical microscope, themicrostructure remains obscure. Even if the reduction ratio of coldworking is about 20%, when the microstructure is observed through atransmission electron microscope image, part of the recrystallized grainboundary before cold working is observed to remain, but it is alreadycovered with a cell structure and it is not possible to determine thegrain size precisely. This fact constitutes a great stumbling block inimproving the properties of a cold rolling material.

[0031] The present invention has discovered that the behavior ofrecrystallization after cold working is correlated with the propertiesof phosphor bronze that is provided with both good bending formabilityand high strength. This correlation is effective for designing anddeveloping materials.

[0032] That is, the copper alloy of the present invention shows adifference between tensile strength and 0.2% yield strength of 80 MPa orless and at the same time has excellent bending formability, and has amean grain size (mGS) after annealing for 10,000 seconds at 425° C. of 5μm or less with a standard deviation of grain size (σGS) of ⅓ mGS orless.

[0033] When cold working is performed after annealing and a reductionratio is increased, the difference between tensile strength and 0.2%yield strength generally decreases, but ductility also decreases at thesame time and cracking is more likely to occur in the bending process.

[0034] However, the present invention has discovered that the reductionin ductility is decreased by adjusting the final annealing conditionbefore the final rolling and cold processing condition before the finalannealing. With conventional phosphor bronze, annealing is performedunder a condition of 425° C.×10,000 seconds where the grains growslarge, and a phosphor bronze product whose mean grain size (mGS) fallsbelow 5 μm is provided with both high strength and excellent bendingformability. More preferably, if the mean grain size (mGS) afterannealing of 425° C.×10,000 seconds is 3 μm or below, the relationshipbetween tensile strength and bending formability is further improved.

[0035] However, even if the mean grain size (mGS) is 5 μm or below, ifgrain sizes are not uniform, the effect is reduced. As will be explainedlater, it is necessary to control the manufacturing method moreprecisely to make a uniform fine grain microstructure. The allowablerange of uniformity should be ⅓ mGS or less as a standard deviation ofthe grain size. This is because when the standard deviation of grainsize (σGS) exceeds ⅓ mGS, the effect of improving bending formability issmall.

[0036] Phosphor bronze having characteristics under these conditions isprovided with press punching formability combined with bendingformability.

[0037] (7) The embodiments in (1) to (4) have improved only the punchingformability, and cannot thereby avoid slight deterioration of bendingformability. Combining the characteristic in (6) can improve both presspunching and bending formability considerably.

[0038] (8) This invention relates to the method of manufacturing ahigh-strength phosphor bronze strip. With regard to a phosphor bronzestrip manufactured by repeating cold rolling and annealing, thisembodiment relates to the method of manufacturing a high-strengthphosphor bronze strip which determines the final cold-rolling and thepreceding final annealing and further the cold rolling process precedingthereto. This embodiment is intended to increase the strength byminiaturization of grains through final annealing.

[0039] The thickness of the material before cold rolling is set tot_(o), the thickness of the material after cold rolling is set to t, andthe reduction ratio X of cold rolling defined by X=(t_(o)−t)/to×100 (%)is determined to 45% or more because if X is less than 45%, it isdifficult to miniaturize the grain size after the final annealing evenif the heat treatment condition of final annealing is adjusted.Furthermore, the mean grain size (mGS) after annealing is determined to3 μm or less and the standard deviation of the grain size (σGS), whichis determined to 2 μm or less because it is necessary to control aheating temperature profile during annealing precisely and make auniform fine grain microstructure. To be accurate, the grain size doesnot show a normal distribution and when the mean grain size (mGS) is 3μm and the standard deviation of the grain size (σGS) is 2 μm, 99% ormore of individual grain size is mGS+3σ, that is, 9 μm or less.

[0040] Moreover, a mixture of grains of 8 μm or greater in size in arecrystallized microstructure is not necessarily desirable, and thestandard deviation of the grain size is preferably 1.5 μm or less.

[0041] The higher the reduction ratio of cold rolling before finalannealing, the smaller the recrystallized grain after the finalannealing is likely to become, but at the same time the behavior ofnucleation and subsequent secondary recrystallization varies a greatdeal, increasing the likelihood to produce duplex grain structure. Thistendency is particularly strong with a copper alloy having a pure coppertype recrystallization structure with high copper concentration. On thecontrary, with phosphor bronze containing 4 mass % or more of Sn,recrystallized gains after relatively strong working are more likely tobe made uniform. It is necessary to optimize the annealing condition,that is, temperature, time and temperature profile for each alloy systemconsidering these aspects, and create the above-describedrecrystallization structure. If either the specification of the meangrain size of 3 μm or less or the specification of its standarddeviation of the grain size of 2 μm or less is not observed, it is notpossible to achieve a high work hardening property during final coldrolling.

[0042] When final cold working at a reduction ratio of 10 to 45% isperformed under conditions with an mean grain size of 3 μm or less andits standard deviation of the grain size of 2 μm or less, a copper alloywith high strength and excellent bending formability results. At areduction ratio of less than 10%, even a conventional copper alloy whosemean grain size after final annealing is approximately 10 μm has goodbending formability and has a small effect of miniaturization of grains.Furthermore, at a reduction ratio greater than 45%, bending formabilitydeteriorates and the range of application as a metallic material such asbent contacts becomes narrower.

[0043] (9) By improving only punching formability, the embodiments in(1) to (4) cannot avoid slight reduction of bending formability.Combining the characteristic in (8) makes it possible to improve bothpunching formability and bending formability considerably.

[0044] (10) This embodiment performs stress relief annealing after finalrolling on the above-described copper alloy and specifies the amount ofreduction in tensile strength with the stress relief annealing, and thisspecification is TS_(a)<TS_(o)−X (reduction ratio of final cold-rolling(%)) where TS_(o) (MPa) is tensile strength before stress reliefannealing and TS_(a) (MPa) is tensile strength after stress reliefannealing.

[0045] Phosphor bronze and nickel silver, etc., maybe subjected tostress relief annealing. Unlike recrystallization annealing appliedbefore final rolling, stress relief annealing is generally practiced on,for example, phosphor bronze for springs (C5210: JIS H 3130), etc., forthe purpose of recovering the ductility (formability) which has beenreduced by cold working and improving spring properties together. Thisstress relief annealing can be applied through a tension annealing line,etc., after final rolling as required. That is, even after stress reliefannealing, the phosphor bronze according to the above-describedembodiment has higher strength and better bending formability thanphosphor bronze manufactured using a conventional technology.Furthermore, when an annealing material of a small grain size issubjected to cold rolling, it is effective to perform stress reliefannealing according to the final reduction ratio to recover ductility.In order to improve bending formability in particular, stress reliefannealing is performed on a cold rolled material of tensile strength ofTS_(o) (MPa) under the condition of TS_(a)<TS_(o)−X, where X % is thereduction ratio of final cold-rolling and TS_(a) (MPa) is tensilestrength after stress relief annealing. For example, in the case of acold rolled material manufactured and hardened up to 800 MPa at a finalreduction ratio of 50%, if this material is subjected to stress reliefannealing until its tensile strength falls below 750 MPa, it is possibleto obtain a material with good bending formability.

[0046] Having now generally described the invention, the same will bemore readily understood through reference to the following Embodiments,which are provided by way of illustration, and are not intended to belimiting of the present invention, unless specified.

[0047] (1) Embodiment 1

[0048] This is related to the embodiments according to Aspects 1 to 4.

[0049] Using the phosphor bronze of the composition shown in Table 1 asa base, S, Mn, Ca, Mg and Al were added thereto, the phosphor bronze ismelted covered with charcoal in the atmosphere, and casted into an ingotmeasuring W 100 mm×t 40 mm×L 150 mm. This ingot was annealed forhomogenizing in an atmosphere of 75% N₂+25% H₂ at 700° C. for one hour,a tin segregation layer formed on the surface was ground and removedusing a grinder and then a chemical analysis was performed. Then, coldrolling and recrystallization annealing were repeated a plurality oftimes as required and a sheet of 0.2 mm in thickness was obtained.Adjustments were made so as not to produce differences in the workhistory by equalizing the reduction ratio of cold rolling before finalannealing, grain size at final recrystallization annealing and thereduction ratio of final cold rolling, etc. Composition, the sum totalof lengths of etching imprints measured by etching the cross-section ofthe sheet, area ratio of copper sulfide phase measured by EPMA andplastic deformation ratio obtained by a shearing test are shown in Table1.

[0050] In contrast to comparative examples, this embodiment shows alower plastic deformation ratio and better press punching formability.TABLE 1 Mn+Ca+Mg+Al Total length of Volume ratio of Plastic CompositionS content content etching imprints copper sulfide deformation No. (mass%) (ppm) (ppm) (mm/mm2) phase (%) ratio (%) Embodiments 1 Cu-4.5Sn-0.15P31 44 6.8 1.7 41 2 Cu-6.2Sn-0.13P 33 37 7.2 1.8 40 3 Cu-8.0Sn-0.14P 3035 7.3 1.8 42 4 Cu-10.0Sn-0.15P 32 41 7.2 1.7 42 5 Cu-8.2Sn-0.14P 21 364.8 1.2 46 6 Cu-8.2Sn-0.15P 22 35 5.3 0.9 44 7 Cu-8.0Sn-0.16P 56 42 9.42 33 8 Cu-8.1Sn-0.14P 93 48 11.4 2.6 31 Comparative examples 1Cu-4.2Sn-0.13P 14 38 3.8 0.4 57 2 Cu-6.2Sn-0.15P 11 42 2 0.3 58 3Cu-8.0Sn-0.14P 22 87 5.1 0.8 55 4 Cu-10.0Sn-0.15P 16 60 3.6 1.1 59

[0051] (2) Embodiment 2

[0052] This is the embodiment according to Aspect 5.

[0053] This embodiment is composed of a phosphor bronze composition as abase and S, Mn, Ca, Mg, Al and Zn as added elements, and a test piecewas adjusted using the same method as that in Embodiment 1 so as not toproduce differences in the work history by equalizing the reductionratio of cold-rolling before final annealing, grain size at finalrecrystallization annealing and the reduction ratio of finalcold-rolling, etc. With regard to bending formability (r/t), a testpiece measuring W 10 mm×L 100 mm was prepared perpendicular to therolling direction, subjected to a W-bending test (JIS H 3110) withvarious bending radiuses and a minimum bending radius ratio (r (bendingradius)/t (thickness of test piece)) without cracking was found. Thebending axis for the W-bending test was parallel to the rollingdirection.

[0054] Among comparative examples, those with a low plastic deformationratio have a large r/t and those with a small r/t have a high plasticdeformation ratio. This embodiment has a low plastic deformation ratioand a small r/t, and is therefore excellent in both press punchingformability and bending formability.

[0055] The results are shown in Table 2. TABLE 2 Mn+Ca+Mg+Al PlasticCompostition S content content Zn content deformation No (mass %) (ppm)(ppm) (ppm) ratio (%) r/t Embodiments 9 Cu-4.0Sn-0.14P 30 44 220 44 0.510 Cu-6.1Sn-0.15P 31 37 228 42 0.5 11 Cu-8.0Sn-0.13P 33 35 217 42 0.5 12Cu-9.9Sn-0.14P 32 41 202 44 0.5 13 Cu-8.2Sn-0.16P 21 36 107 49 0.5 14Cu-7.9Sn-0.15P 24 35 334 47 0.5 15 Cu-8.0Sn-0.13P 55 42 820 35 1.0 16Cu-8.1Sn-0.16P 90 48 730 31 1.5 Comparative examples 5 Cu-4.2Sn-0.13P 1535 212 55 0.5 6 Cu-6.2Sn-0.15P 14 40 300 54 0.5 7 Cu-8.0Sn-0.14P 24 81185 52 0.5 8 Cu-10.0Sn-0.15P 16 63 108 56 1.0 9 Cu-4.1Sn-0.13P 25 381200 59 0.5 10 Cu-6.0Sn-0.14P 80 42 66 32 1.5 11 Cu-8.0Sn-0.15P 24 351070 57 0.5 12 Cu-10.0Sn-0.15P 90 45 75 30 2.0

[0056] (3) Embodiment 3

[0057] This is the embodiment according to Aspect 6.

[0058] With the phosphor bronze of the composition shown in Table 3, atest piece was adjusted using the same method as that in Embodiment 1without adding S, Mn, Ca, Mg, Al and Zn. However, in Embodiment 3, thereduction ratio of cold rolling before final annealing, grain size atfinal recrystallization annealing and the reduction ratio of final coldrolling, etc., were adjusted to produce differences in the work history.The mechanical properties are shown in Table 3.

[0059] Tensile strength (TS: MPa) and 0.2% yield strength (YS: Mpa) wereobtained by preparing a No. 13 B test piece (JIS Z 2201) in parallel tothe rolling direction and carrying out a tensile test (JIS Z 2241) onthe test piece.

[0060] With regard to the grain size, the number of grains completelycut by a line segment of a predetermined length according to theintercept method (JIS H 0501) is counted and an average value of thecutting lengths is considered as the grain size. The standard deviationof the grain size (σGS) is a standard deviation of the grain size. Thatis, a cross-sectional microstructure perpendicular to the rollingdirection is magnified using a scanning electron microscope (SEM image)4,000times, a value obtained by dividing a straight line segment of 50μn in length by a value obtained by subtracting 1 from the number ofintersections between the line and grain boundary is considered as thegrain size. An average of the respective grain size obtained bymeasuring 10 line segments is considered as a mean grain size (mGS) anda standard deviation of the respective grain size is considered as thestandard deviation of the grain size (σGS) according to the presentinvention.

[0061] Compared to comparative examples (conventional materials), thisembodiment has better punching formability and bending formability ifthe strength is the same. TABLE 3 After annealing of 425° C. × Plastic10,000 deform- seconds ation Composition mGS σGS TS-YS TS ratio No (mass%) (μm) (μm) (M Pa) (M Pa) (%) r/t Embodiments 17 Cu-4.2Sn-0.13P 4.9 0.811 606 41 0.5 18 Cu-6.2Sn-0.13P 4.0 0.7 14 730 40 1.0 19 Cu-8.0Sn-0.13P3.9 0.6 8 874 36 1.5 20 Cu-10.0Sn-0.13P 3.5 0.6 11 868 36 1.0 21Cu-4.2Sn-0.13P 3.3 0.6 8 650 38 0.5 22 Cu-6.2Sn-0.13P 3.5 0.7 8 760 350.5 23 Cu-8.0Sn-0.13P 3.6 0.5 5 906 31 1.0 24 Cu-10.0Sn-0.13P 3.5 0.5 11914 33 1.0 Comparative examples 13 Cu-4.2Sn-0.13P 6.5 1.3 25 590 52 1.514 Cu-6.2Sn-0.13P 7.0 2.5 22 667 51 2.0 15 Cu-8.0Sn-0.13P 5.0 1.8 13 80546 3.5 16 Cu-10.0Sn-0.13P 6.0 1.5 24 855 44 2.0

[0062] (4) Embodiment 4

[0063] This is the embodiment according to Aspect 7.

[0064] For the coils of the compositions 1 to 16 of the embodimentsshown in Tables 1 and 2, the test piece was prepared using the samemethod as that in Embodiment 3 by adjusting the reduction ratio of coldrolling before final annealing, grain size at final recrystallizationannealing and the reduction ratio of final cold rolling, etc., toproduce differences in the work history.

[0065] Compared to comparative examples (conventional materials), thisembodiment has better punching formability and bending formability ifthe strength is the same.

[0066] The results are shown in Table 4. TABLE 4 After annealling ofPlastic Mn+Ca+Mg+Al 425° C. × 10,000 seconds deformation Composition Scontent content mGS σGS TS-YS TS ratio No (mass %) (ppm) (ppm) (μm) (μm)(M Pa) (M Pa) (%) r/t Embodiments 25 Cu-4.2Sn-0.15P 31 44 4.5 0.7 13 60139 1.0 (alloy of Embodiment 1) 26 Cu-6.2Sn-0.13P 33 37 4 0.6 14 725 381.5 (alloy of Embodiment 2) 27 Cu-8.0Sn-0.14P 30 35 3.6 0.6 11 870 362.0 (alloy of Embodiment 3) 28 Cu-10.0Sn-0.15P 32 41 3.2 0.5 15 865 341.5 (alloy of Embodiment 4) 29 Cu-4.2Sn-0.15P 31 44 3.3 0.6 8 644 38 0.5(alloy of Embodiment 1) 30 Cu-6.2Sn-0.13P 33 37 3.3 0.5 7 767 33 0.5(alloy of Embodiment 2) 31 Cu-8.0Sn-0.14P 30 35 3 0.4 7 901 30 1.0(alloy of Embodiment 3) 32 Cu-10.0Sn-0.15P 32 41 2.9 0.4 11 905 30 1.0(alloy of Embodiment 4) Comparative Examples 17 Cu-4.2Sn-0.15P 31 44 7.22 27 588 52 2.0 (alloy of Embodiment 1) 18 Cu-6.2sn-0.13P 33 37 7 2.3 25660 52 2.5 (alloy of Embodiment 2) 19 Cu-8.0sn-0.14P 30 35 6.3 1.6 20811 45 3.0 (alloy of Embodiment 3) 20 Cu-10.0Sn-0.15P 32 41 5.0 1.8 25872 45 3.0 (alloy of Embodiment 4)

[0067] (5) Embodiment 5

[0068] The embodiment according to Aspect 8 was verified.

[0069] Table 5 shows the result.

[0070] Comparative examples are conventional examples with the reductionratio of cold rolling before final annealing, and mean grain size atfinal annealing deviating from the present invention. Compared toconventional materials, which are comparative examples, this embodimenthas higher strength and lower r/t and better bending formability. TABLE5 Reduction ratio of cold rolling before After recrystallizationReduction recrystallization annealling ratio of final Compositionannealing mGS (σm) cold rolling TS No (mass %) (%) (μm) (μm) (%) (M Pa)r/t Embodiments 33 Cu-4.2Sn-0.13P 48 2.0 1 30 623 1.5 34 Cu-6.2Sn-0.13P50 1.8 1.2 25 710 1.0 35 Cu-8.0Sn-0.13P 50 1.6 1 25 746 1.5 36Cu-10.0Sn-0.13P 60 1.2 0.7 35 950 40 Comparative examples 17Cu-4.2Sn-0.13P 40 6 2.1 35 602 2.0 18 Cu-6.2Sn-0.13P 40 8.2 2.3 30 6501.0 19 Cu-8.0Sn-0.13P 44 5 2.2 25 682 2.0 20 Cu-10.0Sn-0.13P 40 4.2 2.135 880 4.0 21 Cu-8.0Sn-0.13P 40 2.8 1.9 25 710 2.0 22 Cu-8.0Sn-0.13P 502.8 2.1 25 715 2.0 23 Cu-8.0Sn-0.13P 50 2.7 1.3 5 550 0 24Cu-8.0Sn-0.13P 50 5.0 2.3 10 560 1.0

[0071] (6) Embodiment 6

[0072] The effect of stress relief annealing according to Aspect 10 wastested.

[0073] Table 6 shows the result of the test.

[0074] The test pieces prepared in Embodiments 3 to 5 were subjected tostress relief annealing under various conditions and their mechanicalproperties were evaluated. The amount of reduction of tensile strength(TS) due to stress relief annealing is also shown.

[0075] Embodiments No. 39, 41, 43and 45and comparative example No. 27are materials with tin concentration of 8.0 to 8.2 mass %. In contrastto the tensile strength (TS) of 721 to 850 MPa and bending formability(r/t) of 0.5 in this embodiment, the comparative example demonstrates atensile strength (TS) of 755 MPa and r/t of 1, which shows that thepresent invention has higher strength and better bending formability.Furthermore, Embodiments No. 40, 42, 44 and46, and comparative exampleNo. 28 are materials with tin concentration of 10.0 to 10.2 mass %. Incontrast to the tensile strength (TS) of 820 to 859 MPa and bendingformability (r/t) of 0.5 in this embodiment, the comparative exampledemonstrates a tensile strength (TS) of 830 MPa and r/t of 1.5, whichshows that the present invention has higher strength and better bendingformability as well.

[0076] By applying stress relief annealing as shown above, the materialaccording to the present invention has clearly high strength andimproved bending formability compared to the conventional materialsshown in the comparative examples. That is, the present inventionimproves bending formability if the strength is at a comparable level.Furthermore, stress relief annealing provides a drastic increase in thestrength if the bending formability is at a comparable level. TABLE 6 TSreduced Reduction by stress Plastic ratio of final relief deformationr/t before r/t after Embodiment No. before cold rolling annealing TSratio stress relief stress relief No. stress relief annealing (%) (M Pa)(M Pa) (%) annealing annealing Embodiments 37 Embodiment 17 30 35 571 415 0 38 Embodiment 18 30 30 700 40 6 0 39 Embodiment 19 40 65 809 37 80.5 40 Embodiment 20 30 48 820 36 6 0.5 41 Embodiment 23 40 56 850 31 50.5 42 Embodiment 24 30 55 859 33 4.5 0.5 43 Embodiment 27 40 46 824 357 0.5 44 Embodiment 28 30 35 830 34 6 0.5 45 Embodiment 35 25 25 721 414 0 46 Embodiment 36 35 100 850 35 6 0.5 Comparative examples 25Comparative example 13 30 20 570 52 7 0.5 26 Comparative example 14 3042 625 52 8 0.5 25 Comparative example 15 40 50 755 47 10 1.0 28Comparative example 16 30 25 830 44 8 1.5

[0077] Effects of the Invention

[0078] The present invention can improve strength of phosphor bronzewithout sacrificing bending formability and provide high-levelmechanical properties required of a copper alloy as terminals andconnectors for electronic parts. Furthermore, with high tin phosphorbronze (Cu-10 mass %, Sn-P: CDA52400), the present invention has made itpossible to make its way into the filed of high-strength copper alloys,which is the market monopolized by beryllium copper, etc., into whichphosphor bronze has been conventionally unable to make its way becauseof its inferiority in bending formability.

[0079] All publications and patents mentioned in this specification areherein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference. This applicationhereby incorporates by reference the disclosure of Japanese PatentApplication No. 2002-096387.

[0080] While the invention has been described in connection withspecific embodiments thereof, it will be understood that it is capableof further modifications and this application is intended to cover anyvariations, uses, or adaptations of the invention following, in general,the principles of the invention and including such departures from thepresent disclosure as come within known or customary practice within theart to which the invention pertains and as may be applied to theessential features hereinbefore set forth.

What is claimed is:
 1. A phosphor bronze strip with excellent punchingformability comprising 20 to 100 mass ppm of S, 50 mass ppm or less, intotal, of one, two, or more selected from among Mn, Ca, Mg and Al.
 2. Aphosphor bronze strip with excellent punching formability, wherein thesum total of lengths of etching imprints when a cross-section parallelto rolling direction is etched is 5 mm/mm² or more.
 3. A phosphor bronzestrip with excellent punching formability, wherein a copper sulfidephase exists in a range of 1 to 3% of a microstructure of across-section parallel to rolling direction.
 4. The phosphor bronzestrip according to any of claims 1, 2, or 3, wherein a plasticdeformation ratio when a shearing test is conducted with clearance of 4to 10% is 50% or less.
 5. A phosphor bronze strip with excellent bendingformability and punching formability comprising 20 to 100 mass ppm of S,50 mass ppm or less, in total, of one, two, or more selected from amongMn, Ca, Mg and Al, 100 to 1,000 mass ppm of Zn.
 6. A phosphor bronzestrip with excellent bending formability and punching formability,wherein a mean grain size (mGS) after annealing for 10,000 seconds at425° C. is 5 μm or less, a standard deviation of the grain size (σGS) is⅓ mGS or less and a difference between tensile strength and 0.2% yieldstrength of the cold-rolled phosphor bronze strip is within 80 MPa. 7.The phosphor bronze strip with excellent bending formability andpunching formability according to any of claims 1, 2, 3, or 5, wherein amean grain size (mGS) after annealing for 10,000 seconds at 425° C. is5μm or less, a standard deviation of the grain size (σGS) is ⅓ mGS orless and a difference between tensile strength and 0.2% yield strengthof the cold-rolled phosphor bronze strip is within 80 MPa.
 8. Thephosphor bronze strip with excellent bending formability and punchingformability according to claim 4, wherein a mean grain size (mGS) afterannealing for 10,000 seconds at 425° C. is 5 μm or less, a standarddeviation of the grain size (σGS) is ⅓ mGS or less and a differencebetween tensile strength and 0.2% yield strength of the cold-rolledphosphor bronze strip is within 80 MPa.
 9. A phosphor bronze strip withexcellent bending formability and punching formability, wherein a stripsubjected to cold-rolling at a reduction ratio of 45% or more issubjected to final recrystallization annealing to a mean grain size(mGS) of 3 μm or less and the extent that standard deviation of thegrain size (σGS) of 2 μm or less, and then subjected to final coldrolling at a reduction ratio of 10 to 45%.
 10. The phosphor bronze stripwith excellent bending formability and punching formability according toany of claims 1, 2, 3, or 5, wherein a strip subjected to cold-rollingat a reduction ratio of 45% or more is subjected to finalrecrystallization annealing to the extent that the mean grain size (mGS)of 3 μm or less and a standard deviation of the grain size (σGS) of 2 μmor less, and then subjected to final cold rolling at a reduction ratioof 10 to 45%.
 11. The phosphor bronze strip with excellent bendingformability and punching formability according to claim 4, wherein astrip subjected to cold-rolling at a reduction ratio of 45% or more issubjected to final recrystallization annealing to the extent that themean grain size (mGS) of 3 μm or less and a standard deviation of thegrain size (σGS) of 2 μm or less, and then subjected to final coldrolling at a reduction ratio of 10 to 45%.
 12. The phosphor bronze stripwith excellent bending formability and punching formability according toany of claims 1, 2, 3, 5, 6, or 9, wherein a cold-rolled materialsubjected to final cold rolling at a reduction ratio of X (%) withtensile strength of TS_(o) (MPa) is subjected to stress relief annealinguntil tensile strength TS_(a) (MPa) becomes TS_(a)<TS_(o)−X.
 13. Thephosphor bronze strip with excellent bending formability and punchingformability according to claim 4, wherein a cold-rolled materialsubjected to final cold rolling at a reduction ratio of X (%) withtensile strength of TS_(o) (MPa) is subjected to stress relief annealinguntil tensile strength TS_(a) (MPa) becomes TS_(a)<TS_(o)−X.
 14. Thephosphor bronze strip with excellent bending formability and punchingformability according to claim 7, wherein a cold-rolled materialsubjected to final cold rolling at a reduction ratio of X (%) withtensile strength of TS_(o) (MPa) is subjected to stress relief annealinguntil tensile strength TS_(a) (MPa) becomes TS_(a)<TS_(o)−X.
 15. Thephosphor bronze strip with excellent bending formability and punchingformability according to claim 8, wherein a cold-rolled materialsubjected to final cold rolling at a reduction ratio of X (%) withtensile strength of TS_(o) (MPa) is subjected to stress relief annealinguntil tensile strength TS_(a) (MPa) becomes TS_(a)<TS_(o)−X.
 16. Thephosphor bronze strip with excellent bending formability and punchingformability according to claim 10, wherein a cold-rolled materialsubjected to final cold rolling at a reduction ratio of X (%) withtensile strength of TS_(o) (MPa) is subjected to stress relief annealinguntil tensile strength TS_(a) (MPa) becomes TS_(a)<TS_(o)−X.
 17. Thephosphor bronze strip with excellent bending formability and punchingformability according to claim 11, wherein a cold-rolled materialsubjected to final cold rolling at a reduction ratio of X (%) withtensile strength of TS_(o) (MPa) is subjected to stress relief annealinguntil tensile strength TS_(a) (MPa) becomes TS_(a)<TS_(o)−X.